Category: Machine Shop

Mechanical widgetry

Bafang BBS02: Speed Sensor Alignment

My friend Gee’s bike is a Terry Symmetry, designed for (small) women, which poses challenges when mounting “normal size” components. The Bafang BBS02 speed sensor mount (with a reshaped nut) requires far more clearance between the chainstay and the wheel spokes than the Symmetry has:

Bafang BBS02 Speed Sensor – OEM bracket

The chainstay is nearly parallel to the spokes, so the sensor fits equally poorly anywhere its cable will allow.

The obvious solution is to reverse the mount and stick it to the outside of the chainstay, but it’s not mmmm symmetric: the other end is closed. Use a pull saw to cut off the closed end, stick the sensor post in the other way, and then it fits fine:

Bafang BBS02 Speed Sensor – reversed bracket – top

The sawed-off mount is visible from below:

Bafang BBS02 Speed Sensor – reversed bracket – bottom

It looks fine from the outside:

PXL_20210620_160950653 – Bafang BBS02 Speed Sensor – reversed bracket – left side

Mad props to Bafang for the LED showing when the magnet is properly positioned.

2021-06-21
Bafang BBS02: Drop-bar Throttle Adapter

The Bafang BBS02 package includes a thumb-activated throttle which, like the display, should clamp onto a 22.2 mm handlebar. The one on Mary’s bike fit neatly at the end of the left handgrip:

Tour Easy grips – left installed

There’s no similar location on a drop-bar bike that doesn’t get in the way, particularly on my friend Gee’s bike with narrow bars.

With a display handlebar adapter in hand, this seemed less awful than anything else I had in mind:

Bafang Throttle adapter – front view

That’s the front view, so it’s on the right side in front of the handlebar. I think it’s usable with either a thumb or fingertips from a hand on the top of the bar. The handlebar lacks tape, as mounting the brake sensors poses a challenge.

The view from the rear isn’t too revealing:

Bafang Throttle adapter – rear view

Not too unsightly, but definitely not a standard setup!

2021-06-18

Bafang BBS02: Drop-bar Display Adapter

All of the Bafang BBS02 displays have a compression clamp intended for more-or-less standard 22.2 mm handlebars, as found on typical upright BMX-ish bikes suitable for conversion to e-bikes and, oddly, our Tour Easy recumbents. My friend’s bike has drop-bar handlebars with a 25.4 mm (yes, exactly 1 inch) center section that just isn’t going to fit through that hole.

The least awful solution involved summoning an adapter from the vasty digital deep:

Display adapter mount - solid model — Display adapter mount – solid model

The hole clamps around the handlebar with an M3 SHCS pulling it snug and the display clamps around the peg to hold everything together:

Bafang Display adapter - front view — Bafang Display adapter – front view

There’s not much to see from the side:

Bafang Display adapter - left view — Bafang Display adapter – left view

Those scuffs arrived on the protective plastic film!

The OpenSCAD source code includes some cruft from an idea that didn’t work out quite right:

HandlebarMax = 1*inch;                      // middle handlebar diameter
HandlebarMin = 24.0;                        //  .. tape section

BafangClampID = 22.3;                       // new handlebar diameter


… snippage …

// Handlebar mount for controller

module DispMount() {

ClampRing = [HandlebarMax,HandlebarMax + 2*WallThick,10.0];
ClampOffset = (HandlebarMax + BafangClampID)/2 + 6.0;

DispStudLenth = 16.5;

NumSides = 24;

Tilt = 0*atan2((ClampRing[OD] - BafangClampID)/2,ClampOffset);
echo(str("Tilt: ",Tilt));

    difference() {
        union() {
            hull() {
                cylinder(d=ClampRing[OD],h=ClampRing[LENGTH],$fn=NumSides);
                translate([0,ClampOffset,0])
                    cylinder(d=BafangClampID,h=ClampRing[LENGTH],$fn=NumSides);
            }
            translate([0,ClampOffset,0])
                cylinder(d=BafangClampID,h=ClampRing[LENGTH] + DispStudLenth,$fn=NumSides);
            translate([-ClampRing[ID]/4,-(ClampRing[OD]/2),ClampRing[LENGTH]/2])
                rotate([0,90,0]) rotate(180/8)
                    cylinder(d=ClampRing[LENGTH]/cos(180/8),h=ClampRing[ID]/2,$fn=8);
        }
        cube([Kerf,4*ClampOffset,4*DispStudLenth],center=true);
        translate([0,0,-Protrusion])
            cylinder(d=ClampRing[ID],h=ClampRing[LENGTH] + 2*Protrusion,$fn=NumSides);
        translate([-ClampRing[ID]/2,-(ClampRing[OD]/2),ClampRing[LENGTH]/2])
            rotate([0,90,0]) rotate(180/8)
                PolyCyl(Screw3[ID],ClampRing[ID],8);
        for (i=[-1,1])
            translate([i*ClampRing[ID]/4,-(ClampRing[OD]/2),ClampRing[LENGTH]/2])
                rotate([0,i*90,0]) rotate(180/8)
                    PolyCyl(Washer3[OD],ClampRing[ID],$fn=8);

        translate([-5,25,EmbossDepth/2 - Protrusion/2])
            rotate(Tilt)
                cube([4.5,21.5,EmbossDepth + Protrusion],center=true);

    }

    translate([-5,25,0])
        linear_extrude(height=EmbossDepth)
            rotate(90 + Tilt) mirror([0,1,0])
              text(text="KE4ZNU",size=3.3,spacing=1.05,font="Bitstream Vera Sans:style=Bold",
                   halign="center",valign="center");

}

It’s rock-solid stable: pushing the buttons doesn’t budge it in the least.

2021-06-17

Stylus Tip Restaking

The tip of the much-battered stylus useful for websites presenting tiny phone-hostile buttons appeared in the laundry basket, narrowly avoiding a trip through the washer. The shell’s original all-around swaging had evidently loosened enough to release the tip, so I applied a hammer and punch:

Screen stylus tip restaking

The punch mark (with another on the opposite side) is barely visible, but holds the tip securely in place. Next time I may need more hammer.

2021-06-16

Bafang BBS02 Programming Adapter: CP2102 Version

The last view before sticking the lid in place with hot melt glue:

Bafang BBS02 - CP2102 Programming Adapter — Bafang BBS02 – CP2102 Programming Adapter

The cable on the right goes to the motor controller through the display pigtail cable, sporting colors from a parallel universe.

A (possibly not counterfeit) CP2102 USB-to-serial adapter allows a slightly smaller case than one with the known-fake FTDI adapter and added some identification:

Bafang BBS02 - CP2102 Programming Adapter - case solid model — Bafang BBS02 – CP2102 Programming Adapter – case solid model

It splits along the midline for printing, of course.

The OpenSCAD source code replaces the previous version:

// Programming cable case

ProgCavity = [60.0,18.0,7.0];
ProgBlock = [70.0,24.0,13.0];
ProgCableOD = 4.0;

module ProgrammerCase() {

    difference() {
        hull() {
            for (i=[-1,1], j=[-1,1])
                translate([i*(ProgBlock.x/2 - CornerRadius),j*i*(ProgBlock.y/2 - CornerRadius),-ProgBlock.z/2])
                    cylinder(r=CornerRadius,h=ProgBlock.z,$fn=12);
            }
        translate([-ProgBlock.x,0,0])
            rotate([0,90,0])
                PolyCyl(ProgCableOD,3*ProgBlock.x,6);
        cube(ProgCavity,center=true);

        translate([0,0,ProgBlock.z/2 + ProgCavity.z/2 - EmbossDepth])
            cube(ProgCavity,center=true);
        translate([0,0,-(ProgBlock.z/2 + ProgCavity.z/2 - EmbossDepth)])
            cube(ProgCavity,center=true);

    }

    translate([0,4,ProgBlock.z/2 - EmbossDepth])
        linear_extrude(height=EmbossDepth)
            text(text="Bafang BBS02",
                 size=5,spacing=1.00,font="Bitstream Vera Sans:style=Bold",
                 halign="center",valign="center");

    translate([0,-4,ProgBlock.z/2 - EmbossDepth])
        linear_extrude(height=EmbossDepth)
            text(text="Programmer",
                 size=5,spacing=1.00,font="Bitstream Vera Sans:style=Bold",
                 halign="center",valign="center");

    translate([0,4,-ProgBlock.z/2])
        linear_extrude(height=EmbossDepth)
            mirror([1,0])
                text(text="Ed Nisley",
                    size=5,spacing=1.00,font="Bitstream Vera Sans:style=Bold",
                    halign="center",valign="center");
    translate([0,-4,-ProgBlock.z/2])
        linear_extrude(height=EmbossDepth)
            mirror([1,0])
                text(text="softsolder.com",
                    size=5,spacing=1.00,font="Bitstream Vera Sans:style=Bold",
                    halign="center",valign="center");

}

// Half case sections for printing

module HalfCase(Section = "Upper") {

    intersection() {
       translate([0,0,ProgBlock.z/4])
            cube([2*ProgBlock.x,2*ProgBlock.y,ProgBlock.z/2],center=true);
        if (Section == "Upper")
            ProgrammerCase();
        else
            translate([0,0,ProgBlock.z/2])
                ProgrammerCase();
    }
}

// .. snippage ..

        translate([0,2*Block.x/2 * gap,0]) {

            translate([gap*ProgBlock.x/2,0,ProgBlock.z/2])
                rotate([180,0,0])
                    HalfCase("Upper");
            translate([-gap*ProgBlock.x/2,0,0])
                HalfCase("Lower");
        }

My friend rides about the same way we do, except from a much higher perch, so I’ll start her off with a configuration similar to the one we settled on for Mary’s Tour Easy.

2021-06-15

Garden Sprayer Pivot Repair

A winning entry in the “The Bigger the Blob, the Better the Job” category:

Garden Sprayer – pivot repair

Buried under the epoxy is the flimsy tab with the pivot around which the handle moves. Any sideways force ~~will~~ did snap the tab off flush with the body. I had previously repaired it with solvent adhesive, so something more substantial seemed appropriate.

A closer look shows the edges of the brass flange I formed around the tab to absorb the stress:

Garden Sprayer – pivot repair – detail

It’s pretty much fully depreciated, but if I don’t use the epoxy it will go bad on the shelf, so …

2021-06-14
Bafang BBS02: Speed Sensor Nut Reshaping
A Bafang BBS02 (for a friend’s upright bike) arrived with a deformed speed sensor nut:

Bafang BBS02 – Deformed speed sensor nut – end view

It traveled halfway around the planet while trapped underneath the motor and, if it rode in the top layer or two of containers, the combination of pressure and heat would be irresistible.

The plastic was stiff and I couldn’t force the nut over the connector using as much force as seemed reasonable:

Bafang BBS02 – Deformed speed sensor nut – test assembly

On the upside, the nut just compresses the silicone washer between the connector and the sensor to make a waterproof joint, so it need not have perfect threads or a uniform shape. Once the nut is in place, it will likely never be removed and should never bother anyone else.

Being unwilling to apply a hot-air gun near the cable, I decided to try slowly cold-forming the nut inside a mold:

Sensor Nut mold – solid model

The gap isn’t a kerf: the two halves meet to form a cylindrical pocket. The smaller holes fit a pair of brass tubes keeping the halves lined up while I arrange things:

Bafang BBS02 – Deformed speed sensor nut – clamp detail

A pair of swivel-pad clamps apply the pressure:

Bafang BBS02 – Deformed speed sensor nut – compression clamp

A few days of squashing made it round-er, whereupon I applied the clamp directly against the remaining high point with the other side cradled in the mold. It still doesn’t slide over the connector body, but I’m not in a rush.

Bafang tech support generously sent a speed sensor extension cable from which I can extract a good nut, which will require cutting and splicing the cable from the motor.

I’m still hoping gentle suasion will prevail.

The OpenSCAD source code tucks into the overall file producing various useful bits:
```
// Mold to reshape speed sensor nut

SensorNut = [0,14.4,13.0];
SensorMold = [SensorNut[OD] + 2*WallThick,SensorNut[OD] + 2*WallThick,SensorNut[LENGTH] + WallThick];
MoldSides = 20;
RodOD = 1.6;

module NutMoldBlock() {

    difference() {

        translate([0,0,SensorMold.z/2])
            cube(SensorMold,center=true);

        translate([0,0,WallThick])
            rotate(180/MoldSides)
                PolyCyl(SensorNut[OD],2*SensorNut[LENGTH],MoldSides);
        translate([0,0,-Protrusion])
            rotate(180/8)
                PolyCyl(SpeedOD,2*SensorMold.z,8);

        for (i=[-1,1])
            translate([i*(SensorMold.x/2 - WallThick/2),SensorMold.y,SensorMold.z/2])
                rotate([90,0,0])
                    PolyCyl(RodOD,2*SensorMold.y,6);
    }
}

module NutMold() {
    gap = 1.0;

    for (j=[-1,1])
        translate([0,j*gap,0])
            intersection() {
                translate([0,j*SensorMold.y,0])
                    cube(2*SensorMold,center=true);
                NutMoldBlock();
            }
}

… snippage …

if (Layout == "NutMold")
    NutMold();
```
I haven’t worked on a safet y bike in years!
2021-06-10